Motion sensors have a wide range of applications and are implemented using a wide range of techniques exploiting a wide range of physical principles. Medical applications for motion sensors include diagnosis and treatment of a subject based on the presence, function or location of blood vessels that carry moving blood cells and other constituents. Sometimes the tissue, such as bone, is difficult to penetrate for obtaining the motion measurement. Only a few motion sensors are suitable for such varied medical applications.
One technique that has been used in medical applications is laser Doppler flowmetry (LDF). As stated in Marc F. Swiontkowski, “Laser Doppler Flowmetry—Development and Clinical Application,” Iowa Orthopaedic Journal, v11, pp 119-126 (1991), “Laser Doppler Flowmetry (LDF) is an accurate and reliable method for assessing microcirculatory function. Through a series of in vitro and in vivo experiments, LDF output has been shown to be reproducible and to correlate with bone blood flow as estimated by other methods. The utility of the method in assessing meniscal, tendonous, and ligamentous perfusion has also been demonstrated. LDF has proven potential in clinical research in osteonecrosis, osteomyelitis, fracture healing, and other areas.” LDF has also been applied to neurosurgery, dermatology and dentistry. However, these devices suffer from low signal to noise ratio and low spatial resolution compared to blood vessels of interest during many diagnosis and treatment procedures.
Another technique used in medical applications is Doppler optical coherence tomography (DOCT). Optical coherence tomography (OCT) is an optical signal acquisition and processing method. It captures micrometer-resolution, three-dimensional images from within optical scattering media (e.g., biological tissue). Depending on the properties of the light source (superluminescent diodes, ultrashort pulsed lasers and supercontinuum lasers have been employed), optical coherence tomography has achieved sub-micrometer resolution (with very wide-spectrum sources emitting over a range of wavelengths about 100 nanometers wide, 1 nanometer, nm, =10−9 meters). Commercially available optical coherence tomography systems are employed in diverse applications, including diagnostic medicine, notably in ophthalmology where it can be used to obtain detailed images from within the retina. Recently it has also begun to be used in interventional cardiology to help diagnose coronary artery disease. Determining the Doppler shift in the returned signal due to motion of the optical scatterers in the sample, turns the OCT into a 3D imaging DOCT motion sensor. However, these devices are expensive, complicated, unwieldy and difficult to use when diagnosing or treating patients.